Brian is expanding his store to include antique goods. What should he do if there isn’t a unique product identifier available?

Some products genuinely have no manufacturer-assigned identifier — antiques, one-off pieces, handmade goods — and Google provides an explicit way to declare that rather than leaving merchants to improvise. Setting the identifier exists attribute to false tells Merchant Center the omission is intentional, so the item is processed without warnings about missing GTIN or MPN data. The important principle is that you declare the absence honestly instead of inventing a value.